package datastructure.segmenttree;

/**
 * @author XY
 * @version 1.0.0
 * @ClassName NumArray2.java
 * @createTime 2021年12月20日 19:28:00
 */
public class NumArray2 {

    //sum[i] 存储前i个元素的和，sum[0]= 0
    //sum[i] 存储nums[0,,,i-1]的和
    private int[] sum;

    private int[] data;

    public NumArray2(int[] nums){
        data = new int[nums.length];
        for (int i = 0; i < nums.length; i++) {
            data[i] = nums[i];
        }
        //因为sum[0] =0 所以会产生一个偏移量
        sum = new int[nums.length+1];
        sum[0] = 0;
        for (int i = 1; i < sum.length; i++) {
            sum[i] = sum[i-1] + nums[i-1];
        }
    }
    public void update(int index,int val){
        data[index] = val;
        for (int i = index+1; i < sum.length; i++) {
            sum[i] = sum[i-1] + data[i-1];
        }
    }

    public int sumRange(int i, int j){
        return sum[j+1]-sum[i];
    }
}
